The invention relates to a method for coating elongated metal blanks.
In the series of books "Produktionstechnik heute" [Production Engineering Today] (published by Prof. H. J. Warneke), a description of so-called sliding grinding is given in volume 14, Entgraten, Theorie, Verfahren, Anlagen [Deburring, Theory, Methods, Apparatus] by F. Schafer on pages 93 to 98. A multiplicity of blanks located in a rotationally driven drum slide against one another and against added abrasive media during the rotary movement of the drum. The manner in which they slide against one another is dependent on the speed of rotation. At low speeds, sliding against one another takes place. As from a certain speed, the sliding zone breaks down; workpieces and abrasive media described there strike one another. This and the sliding against one another effects a surface-removing effect.
In the case of the method of the type in question, blanks which have at least two portions of different cross section aligned axially, one after the other, are treated. In a chemical electroplating bath, particles of a hard material are embedded into a metallic delimiting layer on the surface of a first portion which has indentations or the like, the particles projecting from the surface of the layer. The exposed surfaces of a second portion remain to the greatest extent free from hard material particles. The exposed surfaces may be the circumferential surfaces of a cylinder. The base of the cylinder may be a circular surface, an oval surface or a hexagonal surface. The base of the cross section of the portion having the indentations may have a serrated or star-shaped contour. The tooth or star flanks of this portion are to be provided with an embedding of hard material particles. The application of hard material particles to reduce the wearing of workpieces or to increase friction is known in particular in the case of heavy-duty machine parts and also in the case of tools. It is also known, however, to reduce by such measures the susceptibility to wear of portions of other types of metallic objects that are subject to friction or pressure. In the case of known methods, regions of the workpieces that are not to be coated must be covered by means of lacquer or the like. For example, laid-open patent application 29 20 593 shows a method by which particles are introduced into a metal surface by means of locally supplying current. From patent specification 28 55 054, a method is known in which the stator blade of a turbine is coated with a layer of metal with incorporated foreign particles. In this case, only the portions of the blade covered by a clamping device remain uncoated.